I've been using the Cosrx Blackhead Power Liquid for more than a month, and I really like it. It is a gentle BHA, and hasn't caused any drying or irritation on me at all. I'm able to use it twice a day now, with no problems at all. It doesn't provide results as fast as some other BHA's might; but that's the trade off given its so gentle.

It does smell a bit metallic, though that fades as it dries. It also leaves a weird greasy-yet-sticky finish as it's being absorbed; but after about 10-15mins of wait time, the finish is fine. You only need 1-2 pumps to cover the entire face and onto the neck, so it's a pretty good value for the size.